8.3.3 Changing Media Types

8.3.3 Changing Media Types

The media type (audio, video, etc.) for a stream MAY be changed. It is RECOMMENDED that the media type be changed (as opposed to adding a new stream), when the same logical data is being conveyed, but just in a different media format. This is particularly useful for changing between voiceband fax and fax in a single stream, which are both separate media types. To do this, the offerer creates a new media description, with a new media type, in place of the description in the previous SDP which is to be changed.

The corresponding media stream in the answer is formulated as described in Section 6. Assuming the stream is acceptable, the answerer SHOULD begin sending with the new media type and formats as soon as it receives the offer. The offerer MUST be prepared to receive media with both the old and new types until the answer is received, and media with the new type is received and reaches the top of the playout buffer.